The present invention relates to a speech communication system and a talker right reservation method used for the system.
For example, reference 1 (JP 2003-526275) discloses a PoC (Push-to-Talk over Cellular) system based on VoIP (Voice over IP) which allows speech communication between portable terminals on an IP (Internet Protocol) network. In this PoC system, one-to-many speech communication can be performed by using a packet network. However, two or more persons cannot be simultaneously talk. A given person who wants to talk waits until the currently talking person finishes speech, and begins to talk after acquiring the talker right.
The manner of using PoC in a portable terminal is similar to the method of using a transceiver. When a talker keeps the talker right by continuously pressing a dedicated key, uttered speech data is sent to another portable terminal. The user of another portable terminal cannot utter speech but can only receive speech. When the talker right holder releases the dedicated key, the talker right is released. After the right is released, a portable terminal whose dedicated key is pressed first acquires the talker right, and its user can utter speech through the portable terminal.
The talker right in PoC is managed by a PoC server. For example, the PoC server registers members, comprehends participation enable information such as “absence” and “presence” of members and the like (presence function), and assigns the talker right (floor control).
In the above PoC system, in order to acquire the talker right, a talker right acquisition notification must be transmitted to the PoC server after the talker right is released (no one is talking). However, a given user cannot acquire the talker right and cannot utter any speech if another user transmits a talker right acquisition notification ahead of the given user even while no one is talking as well as while someone is talking. Furthermore, if a given user keeps talking and does not release the talker right, other users cannot utter any speech and have no means for sending an intention to utter speech.